So-called optical touch contact switches for glass ceramic hobs are known, for example, from DE 197 00 836 C1, which operate according to the reflected light barrier principle. Below a transparent glass ceramic plate is located such a reflected light barrier with a transmitter and a receiver. If over the same a finger is placed on the glass ceramic plate, light is reflected from the transmitter to the receiver and can be evaluated as an operation. This has proved satisfactory as an advantageous method, but only in the case of covers having the corresponding light transmittance or opening. However, it is disadvantageous that as a result of the arrangement there can only be a maximum of one touch contact switch per light barrier. This leads to relatively high costs, particularly if for certain control units, for example, for dishwashers or hobs, a larger number of touch contact switches is required.
It is also disadvantageous that the contact surface for the finger is located on the hob. This takes up space which in certain circumstances could be used for other purposes. There are also, in part, inhibitions by users against placing a finger on the hob, even if located at a cool point.